While there is room for a range of interpretations, my take on the totality of research is that there may be a small beneficial effect to CHD [coronary heart disease] (through raising HDL or some other mechanism) to light to moderate alcohol consumption, but this benefit has not been clearly established. Further, any such small effect is likely counterbalanced by many negative health effects associated with regular alcohol consumption. And in any case there is no evidence that for any individual taking up regular alcohol consumption is of any health benefit. Further, I think the small effects being seen in these studies are overshadowed by possible confounding factors and the weaknesses of observational studies.
For some context: Dr. Novella is discussing a recent study which examined late-life alcohol consumption and 20-year survival, and which has been garnering some media attention. Unsurprisingly, this sort of media buzz seems to happen whenever any scientific paper suggests that something that we like may actually be good for us. The evidence is usually weak, but is distorted by the media sufficiently to convince the average person that copious consumption of Guinness and Snickers bars will make him or her immortal. We seem to have a tendency to focus on scientific findings that tell us what we want to hear. Go figure.
But I digress. Dr. Novella continues:
Taken at face value, these results indicate that moderate regular alcohol consumption had the lowest mortality, followed by light drinking, then heavy drinking, and then non-drinkers. This last bit is the surprising result, as prior studies have always shown that heavy drinkers have the highest mortality. Of course, that is also the bit that press reports latched onto – heavy drinkers outlive non-drinkers. The effect is tiny once confounders are removed (51% increase in mortality over moderate drinkers for abstainers and 45% for heavy drinkers), but the effect remains.
Given the totality of existing research this is the part of this study that to me says the results are not reliable. It is far easier to believe that there are missing confounding factors in this study or some systematic bias in data analysis rather than that heavy drinkers outlive non-drinkers, despite a large amount of prior research that says the opposite.
I recommend reading his full critique here. But don't neglect the actual study itself, of course.